The invention relates to a method for suppressing the formation of oxygen gas bubbles at the contact interface between a glass melt and a component of a glass melting apparatus with the component consisting of a precious metal. The component is especially the precious metal lining of a feed channel. The characterization xe2x80x9cprecious metalxe2x80x9d includes in this context: platinum, gold, rhenium, all other metals of the platinum group, the alloys of the above-mentioned metals and the above-mentioned metals and alloys in a dispersion oxide enhanced form.
Glass melts always contain a certain water portion which splits into a more or less large percentage of hydrogen and oxygen at the usual glass melt temperatures. The precious metal, which is used for the lining of parts of a glass melt apparatus, is permeable for hydrogen. For this reason, the migration of hydrogen at the phase boundary between the precious metal and the glass melt leads to an enrichment of oxygen which is taken up in the glass melt in the form of small bubbles whereby the quality of the generated glass products can be significantly affected. The occurrence of gas bubbles at the phase boundary between the precious metal and the glass melt has been known for a long time without effective measures being suggested until now in order to significantly improve quality and yield of the generated glass products. This is so especially because precious metal parts must be mounted downstream of the usual purification devices with which glass bubbles can be removed from the melt.
The oxygen partial pressure of a glass melt can, for example, be measured via electrodes dipped into the melt, for example, as in accordance with German patent publication 4,324,922. The electrodes are connected to each other via a voltage measuring apparatus. As explained in U.S. Pat. No. 4,603,980, the temperature and the electric resistance of a glass melt can also be measured in that high frequency alternating currents are applied. With both measuring methods, one should note that no current can flow in the glass melt during the measurement in order not to change the characteristics of the glass melt by the measurement.
In German patent publication DD-PS 201,297, an arrangement for electrically melting glass is disclosed. A high frequency alternating voltage is applied for heating the trough. The sequence of the purification is influenced by blowing gaseous oxygen directly into the melt with the aid of nozzles.
It is an object of the invention to suppress the formation of oxygen gas bubbles at the contact interface between a glass melt and a component of a glass melt apparatus made of precious metal, especially of the precious metal lining of a feed channel.
Surprisingly, it has been shown that this object can be achieved when one electrically connects the part made of precious metal to an electrode (or several electrodes) which is arranged in the glass melt in spaced relationship to the part made of precious metal and when one generates a potential drop between the electrode and the precious metal part in such a manner that a current flows. If an adequately large electrical negative potential difference referred to the glass melt is maintained at the component made of precious metal, then the oxygen is ionized which remains after migration of the hydrogen through the precious metal wall, that is, the oxygen is converted into negatively charged O2xe2x88x92 ions which (other than neutral oxygen molecules) dissolve in the melt in an unlimited quantity and do not bunch to form gas bubbles.
Extensive experiments have shown that the component of oxygen bubbles in the finished glass product can be suppressed down to small non-damaging residual quantities with the measures provided by the invention and that quality and yield of glass production can be considerably increased.